FIG. 6 shows an example of a laminated thin film type magnetic head using an Fe-Si-Al alloy magnetic film, which has recently been used suitably as video heads, computer heads, etc. The structure of this head will now be described briefly.
As shown in FIG. 6, the laminated thin film type magnetic head 1 has a pair of magnetic core halves, i.e., an I core 2 and a C core 4, each of them having a laminated thin film obtained by depositing an Fe-Si-Al alloy thin film 100 on a ceramic substrate, for instance. The I and C cores 2 and 4 have their mating surfaces bonded together via a gap 6. Generally, in such a magnetic head, a chamfered portion or an apex portion 8 is formed adjacent the gap 6 by machining in order to obtain magnetic flux concentration. To bond core halves toughly together this portion is filled with apex glass 10. The structure is then subjected to further processing depending on the purpose, such as for a computer or for a video.
The prior art magnetic head 1, used as a composite type slider of a hard disk drive, is usually classified into two large types determined by the shape of the apex portion 8. In one type of magnetic head, as shown in FIG. 7, the apex space 8 comprises a chamfered portion 12, which is formed in the C core 4 such as to have apex angle .alpha., usually around .alpha.=45.degree., at a position (i.e., apex) with a predetermined gap depth D, and another chamfered portion 14, which is formed as desired in the I core 2 such as to have an angle .theta., usually around .theta.=45.degree. (this magnetic head being hereinafter referred to as "A type magnetic head"). In the other type of magnetic head, as shown in FIG. 8, the apex portion 8 comprises chamfered portions 16 and 18 both formed in the C core 4 with an apex angle .alpha. of substantially 90.degree. and an apex length of T (this magnetic head being hereinafter referred to as "B type magnetic head").
In the A and B type magnetic heads of the above structures, it is well known in the art that, as will be understood from FIG. 9, in the B type magnetic head (FIG. 8) the magnetic flux saturation takes place first not in the gap but in the vicinity of the contact between the chamfered portions 16 and 18, so that the field gradient formed by the gap is substantially fixed irrespective of the increase of magnetomotive force. In the A type magnetic head (FIG. 7), on the other hand, the magnetic flux saturation takes place first at the C core beside the gap, thus giving rise to the so called "roll-off" phenomenon, that is, reduction of the field gradient formed by the gap with magnetomotive force increase. This means that, the A type magnetic head has a problem in recording demagnetization that the reproduction output is reduced by increasing the recording current.
FIG. 9 shows the field gradient which are calculated with a floating level of 0.1 .mu.m, a switching field of 1,600 Oe and a gap depth of 4 .mu.m. The field gradient is a gradient of the recording magnetic field from the head, with respect to the magnetomotive force, corresponding to the magnitude of the switching field of magnetic medium at a position spaced apart a distance corresponding to the floating level.
Comparing the magnetic heads of both types in the reading (or play back) efficiency (.eta.) in the gap, i.e., .eta.=(gap length.times.magnetic field intensity in gap)/(magnetomotive force in ampere-turns), as will be seen from Table 1 below, it was found that B type magnetic heads has the following problems. Namely, the B type magnetic head is inferior in the play back efficiency to the A type magnetic head irrespective of the gap depth (D) so that it can not provide sufficient play back voltage.
TABLE 1 ______________________________________ Gap depth D A type B type ______________________________________ 1 .mu.m 84.9% 69.8% 4 .mu.m 64.9% 60.1% 10 .mu.m 59.1% 56.1% ______________________________________
It was thus found that the shape of the apex portion 8 has great influence on the magnetic properties of the magnetic head 1.